The invention relates to a workpiece abutment for machine tools, especially a rigs fence stop for panel saws having a tilting saw blade, comprising an abutment bar disposed parallel to a tool plane, which can be detachably fixed to a support, which can be moved transversally to the tool plane on and fixed to the machine frame. The abutment bar can be oriented in one of two positions swivelled by 90.degree. in relation to one another around the longitudinal axis of the bar, whereby in a first position the abutment bar presents an abutment face of lesser height to the tool and in a second position presents an abutment face of greater height in comparison thereto to said tool. A stop on the machine frame interacts with a counter-stop on the support to limit the approach of the support to the tool.
By means of so-called abutment, workpieces are positioned on machine tools, such as panel saws, so that precise machining can be performed. With some panel saws the saw blade can be tilted so that longitudinal cuts can be performed at a certain angle.
With such cuts the blanks to be machined are brought to abut the so-called rip or parallel fence, the distance of which from the tool plane can be varied. If abutment bars are used, which make available abutment faces of varying heights depending on the position, so that it is possible to cut narrow workpieces even with a tilting saw blade, there is the difficulty of limiting the approach of the support with the abutment bars of varying widths at varying distances of the support from the tool in order to prevent contact between the abutment bar and the tool in each position of the abutment bar and to guarantee a minimum distance of the abutment bar of 2 mm for example to the tool.
The object of the invention is to provide a workpiece abutment of the type mentioned at the beginning in which the approach of the support and thus of the abutment bar to the tool in both positions of the abutment bar is limited in a particularly safe and simple manner.
The problem is solved in accordance with the invention in that on the machine frame are disposed two stops at different distances from the tool and which interact with a counter-stop adjusted to one of the stops in dependence on the position of the abutment bar.
In this manner in each position of the abutment bar on the machine frame the stop which is automatically activated is that which ensures that the approach of the abutment bar to the tool is limited to the minimum distance.
In a particularly advantageous embodiment of the invention the counter-stop consists of a part movably mounted on the support, which in the first position of the abutment bar assumes a first position in which it is adjusted to interact with the stop farther from the tool, while in the second position of the abutment bar it assumes a second position in which it interacts with the other stop, which is a shorter distance from the tool. The advantage lies in the particularly simple construction of the counter-stop in the form of a part movably mounted on the support.
In a purely mechanical refinement of the invention two of the lateral faces of the abutment bar comprise T-shaped grooves for the attachment of the abutment bar to the support. The counter-stop is an eccentrically mounted bar freely rotating around a horizontal axis, which in the second position of the abutment bar on account of gravity dips partially into one of the T-shaped grooves so that it can travel past the farther stop to the stop disposed laterally staggered in relation thereto. In the first position of the abutment bar this eccentric bar is swivelled into its first position, in which it interacts with the farther stop.
According to an alternative embodiment of the invention, the counter-stop can be moved by means of an electric motor to activate one of the stops by controlling the electric motor by signals of an electro-mechanical sensor, which provides signals varying in accordance with the position of the abutment bar.
Particularly great operating comfort is achieved with an embodiment in which an electronic measurement and display unit determines the relative position of the support in relation to the machine frame and the value of the distance of the stop face from the tool is displayed, and in which an electro-mechanical sensor provides different signals according to the respective position of the abutment bar and supplies them to the measurement and display unit. With a change in the position of the abutment bar, the actual distance of the abutment face from the tool is therefore automatically indicated.
The stops on the machine frame can be advantageously moved so that they can be exactly adjusted in each individual case.
A preferred exemplified embodiment of the present invention is described below with reference to the attached drawings.